In recent years, developments towards Wafer-level Chip Size Package (WL-CSP) or 3D packaging have been progressed to achieve a high-density integration, miniaturization, thinning, and weight reduction of package in the field of IC packaging. In this field, an epoxy resin, polyimide, polybenzoxazole and a benzocyclobutene (BCB) resin which are the existing sealing polymers have been used as a sealing polymer. It is, however, required to lower the curing temperature and form a thick film as well as to achieve a high insulation, an excellent heat resistance, a good chemical resistance etc. in Wafer-level Chip Size Package, 3D packaging, and the like. Furthermore, a matter to be achieved in Wafer-level Chip Size Package (WL-CSP) or 3D packaging is a matching between the thermal expansion coefficient of an underlayer material and the thermal expansion coefficient of a material coated on the underlayer. When the difference between these thermal expansion coefficients becomes large, a problem of curvature occurs.
The consistency of the thermal expansion coefficient significantly influences the reliability of package and it also affects the device life. The curvature of the sealed wafer causes problems in each manufacturing process of the wafer sealed with a sealing material, such as a conveyance process, a polishing process, a test process, and a dicing process, at manufacturing of a package. It is, therefore, hoped that the sealing film material and the insulation film material, which are used in Wafer-level Chip Size Package and 3D packaging, have a thermal expansion coefficient of ppm (40×10−6/° C.) or less, specifically. As polyimide and polybenzoxazole are organic polymers, the thermal expansion coefficients thereof are essentially large. For solving this problem, it was proposed to prevent the curvature of the package by lowering the modulus of elasticity of the sealing film in Wafer-level Chip Size Package (see the patent document 1 below). In this proposal, sealing films were formed by curing a modified polyalkylene oxide compound which has an alkoxysilyl group at its terminal together with an epoxy resin or the like. However, the average thermal expansion coefficient thereof is about 100×10−6/° C.
In addition, the introduction of a silicon element into the polymer lowers the thermal expansion coefficient as the intermolecular force of a Si—O bond is essentially larger than that of a C—C bond. Therefore, the introduction of a silicon element to a polyimide skeleton was studied (see the non-patent document 1 below). However, no photosensitive material having a low thermal expansion coefficient such as 40×10−6/° C. or less as mentioned above, being able to form a thick film, and being excellent in properties such as a heat resistance and a chemical resistance has been found so far.